Cyclone season may be a fizzer
SUNDAY AUGUST 26, 2012
Cyclones are more numerous and of greater magnitude when perigee (the day in the month that the moon is closer to earth) occurs around the latitude of the equator. This happens around two periods in the 8.85-year cycle of changing lunar latitude of perigee positions.
From July 1935 to April 1936 perigees were at or near the equator, and the cyclone of February 1936 was called the most destructive storm to hit New Zealand in the 20th century. A depression crossed the North Island on 2nd/3rd of February 1936 bringing widespread heavy rain and causing every major river in the North Island to flood.
Perigees were also near-to-over the equator between 1966 and 1968. That too, was a black year for NZ. In April 10, 1968, Cyclone Giselle brought flooding and destructive winds to many parts of New Zealand, and the sinking of the inter-island ferry Wahine in Wellington Harbour with the loss of 51 lives.
Perigees were about the equator from 1974 until the following year. On Xmas Eve 1974, Cyclone Tracy blew away Darwin. The moon was sitting on 12degN that day, and Darwin is sited at 12deg S.
Between Feb 1988 and Nov 1989 the moon was averagely closer to the equator than its northern or southern points when Cyclone Bola struck NZ on 7 March, 1988.
Not every perigee brings cyclones and not all cyclones fit a known pattern, but sufficient do to warrant some declaration of predictable trends. Magnified heat from the equatorial belt can pick up more ocean moisture and this occurs mostly at the perigee time of the month.
The southward-trekking perigee can then deliver turbulence to the southern ocean. Conversely, when perigeal moons creep northwards cyclonic hurricanes strike targets in the northern hemisphere.
One example of this was Hurricane Katrina that struck New Orleans on Aug 29, 2005. The moon was at 28degN that day and New Orleans is 29degN.
After March 2007 perigee started moving north of the equator. Tropical cyclones in the southern ocean had become relatively scarce, still occurring 2008-2010 but in fewer numbers. On the day of third closest perigee for 2008, 6 May, Cyclone Nagris struck Burma. That day the moon’s latitude was 22N, and Myanmar (Burma) sits at latitude 22N.
Late in 2008 the perigeal moon was at its northernmost, the first time since January 2000. Perigees at northern declination bring a lot of rain to NZ, for example the Turangi flood fatality in April 2008 which was within days of a powerful northern declination perigee.
Destruction from cyclones diminishes at north and south declinations, making 2007 the last seriously destructive until 2011. In 2009, perigees started drifting south again to lie between northern declination and equator, and so did tropical cyclones, arriving in the first week of February and the last week in March.
March 2010 saw perigees once more equatorial, and cyclone numbers resuming. By mid 2010 the Pacific was at risk in the form of cyclonic activity around Samoa and Tonga. Then, beginning December 2010 and through the first few months of 2011 cyclones started to develop and catch media attention only to slip away to the northeast before bringing too much damage to our shoreline. Surfies were delighted.
In 2012 we were only at risk until perigees shifted away from the equator heading southwards after March.
In June 2013 the closest perigee for the whole year will be at southern declination. It means that 2013 is not expected to be significant for cyclones in the southern hemisphere. Perigees do not sit astride the equator again until after March 2015, which may again be a hurricane season for the Caribbean and eastern seaboard of the US.
So this coming season should be mostly light for cyclones, with systems developing late but petering out quickly and ending up as rain systems. Few may get named. January may see one unusual monsoonal depression intensifying into cyclonic strength as it traverses through the inland and eastern parts of Australia and then NZ in the last week.
However most low pressure systems forming on the east of Queensland this time around are not expected to become more than tropical low pressure systems.
One cyclonic system may affect Western Australia in early March. Another possibly reaches low grade cyclonic status near the Queensland coast in mid-March.
For NZ there may also be a handful of threats that turn to fizzers, with wet conditions in the second week of February and the prospect of a wet March for some, particularly the final 10 days, with chances of widespread heavy rains and flooding.
Western science is answerable to Christianity which still paints a pagan moon. Not so for non-Western and indigenous cultures, which have for hundreds of years asserted that certain moon positions can correlate with extreme events. Perhaps when the politics of cultural and religious differences lessen, our own sciences may re-explore the cycles of moon and weather
© Ken Ring 2012